In the US, the expected statistical figures for breast cancer in 2013 are estimated at approximately 230,000 new cases and 40,000 deaths. The mortality rate can be lowered if breast cancer could be detected in an earlier stage. Screening with X-ray mammography has been the gold standard for the early detection of breast cancer. However, in about 40% of the screening population the women typically more than 50% of their breasts made up of dense fibro-glandular breast tissues that tend to obscure abnormalities in X-ray mammograms. Recent clinical studies show that this “dense breast” gap could be economically and sufficiently dealt with using breast ultrasound, particularly automated three-dimension (“3D”) breast ultrasound. Currently, the only breast ultrasound system that received USFDA approval for breast cancer screening is an automated 3D breast ultrasound system using a chestward compression scanning procedure.
There are two major challenges facing any practical breast cancer screening modality. The first challenge is cost, which can be measured as the cost of the actual examination and assessment of the results, and as the cost per detected cancer. Since breast cancer has a very low prevalence rate such that one cancer is generally found in 200 to 300 asymptomatic patients screened, the per patient screening cost must be kept low, currently typically to the range of $100-$200 in the U.S., in order to achieve a reasonable cost per cancer detected (i.e. $20,000 to $60,000 range). This cost range is generally translated into limiting typical reading/interpretation time to about 3 minutes per patient, using an automated scanning system with a throughput of over 2,000 patients per year. For screening X-ray mammography, where only 4 new images are generated per patient at a screening examination in U.S. practice, this 3-minute interpretation time requirement is relatively easily met. However, for current commercial breast ultrasound screening examinations, where over 1,000 new two-dimensional (“2D”) images obtained by scanning in substantially axial direction under chestward compression (often called “original” images) are typically generated per patient, the 3 minutes of reading/interpretation time limit is very difficult to meet. An associated rapid reading method is used by configuring the original axial images first into coronal thin-slice images and then into composite coronal thick-slice images, e.g., 2-30 coronal thin-slice images into one thick-slice image, so that a user can better search for abnormalities and better manage the reading/interpretation time. See for example U.S. Pat. No. 7,828,733, where the coronal thick-slices method is discussed. However, this method is still not quite fast enough, nor could it satisfactorily solve the “oversight” challenge described immediately below.
The second major challenge of breast cancer screening is the oversight, where obvious cancers are overlooked. A delay in cancer detection due to oversight can cause the cancer to progress to a more advanced stage resulting in decreased patient survivability and increased treatment cost. This problem is particularly serious when trying to read/interpret breast images quickly. A study on blind re-reading of 427 prior screening x-ray mammograms, which were taken a year before the cancer detection, published in Radiology (by Warren-Burhenne et al., 2000, Vol. 215, pages 554-562), reports that as many as 115 (or 27%) of the cancers could have been detected a year earlier and should be classed as oversights. In order to reduce the oversight problem, commercial computer-aided diagnosis (“CAD”) systems have been developed for X-ray mammography screening. Development of clinically useful x-ray mammography CAD was no trivial matter, as the CAD must achieve sensitivities close to that of human readers. The development was undertaken by several commercial firms, some in collaboration with universities and national laboratories, over many years, and is believed to have consumed over $100 million in combined developmental cost. The CAD's impact is clearly visible—after 10 years of its commercial introduction, as reported by a study published in JACR (by Rao et al., 2010, Vol. 7, pages 802-805) by year 2008, 75% of the screening x-ray mammograms were read with CAD assistance.
In the known commercial automated 3D breast ultrasound systems, the ultrasound beam is generally directed chestwardly during the scan while the breast is generally compressed chestwardly. This method has many advantages over the earlier non-chestward-compressed ultrasound scanning method proposals, such as a method that clamps the breast between vise-like scanning plates, as in standard x-ray mammography. The advantages of chestward scanning include: improved patient comfort, thinner breast tissue slices imaged during the scan, and the possibility of employing higher ultrasound frequency resulting in greater image quality. This is discussed in more detail in U.S. Pat. No. 7,828,733. A composite coronal thick-slice method (2-20 mm in slice thickness), which could be used as a guide or road map to aid the search for abnormalities, is also discussed in U.S. Pat. No. 7,828,733, as is the possibility of a full-breast composite image 2502 that preferably is a CAD enhanced expression of the sonographic properties of substantially the entire breast volume, i.e., all of the tissue imaged by the volumetric ultrasound scans, and of enhancing lesions according to their likelihood of malignancy (or other metric of interest). The thick-slice coronal image has been proven helpful as a road map in current commercial automated 3D breast ultrasound systems. In commercial systems, a popular slice thickness of the coronal thick slice is believed to be 2 mm, which is selected for reasons of good image quality and less chance to miss smaller lesions or abnormalities. Slice thickness down to 0.5 mm also is believed to be used.
In commercial automated 3D breast ultrasound screening systems using chestward compression scans, for each patient, several scans are typically made on each breast, for example 2-5 scans, although in some cases it can be a single scan and in some cases more than 5 scans. Each typical scan generates about 300 new images. Thus, 1,200 to 2,400 or more new images can be generated for each patient. With the manifold, e.g., 300 to 600-fold increase in the number of new images over screening x-ray mammography, readers can encounter even more oversights than the 27% or so that can be encountered in screening x-ray mammography. Thus, efficient methods and systems should be developed to better manage both the reading/interpretation time as well as the oversight problems before breast ultrasound screening could be more broadly employed to help more women. Since the worldwide commercial introduction of automated 3D breast ultrasound using chestward compression several years ago, radiologists at hundreds of facilities around the world have been struggling to read/interpret the huge volume of breast ultrasound images per patient study. At the present time, it is believed that only the best readers, even using the composite 2 mm coronal thick-slice image as road maps, are able reach the 3 minutes practical limit per patient, while the majority of the readers are averaging more than 5 to 8 minutes per patient. No published studies on the “oversight” in current commercial automated 3D breast ultrasound are known, but one could venture to guess that the oversight rate could not have been below that found for screening mammography, i.e., more than the reported 27%.
The subject matter claimed herein or in a patent issuing from this patent specification is not limited to embodiments that solve any particular disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.
All the publications, including patents, cited throughout this patent specification, are hereby incorporated by reference.